Back to Subject

Unit 9: Genomic DNA isolation - Practice Quiz

BTY559 — Biotechnology Laboratory-Ii 60 Questions
0 Correct 0 Wrong 60 Left
0/60

1 What does the abbreviation CTAB stand for?

Isolation of Plant genomic DNA using CTAB method Easy
A. Cetyl Trimethyl Ammonium Borate
B. Cetyl Trimethyl Ammonium Bromide
C. Carboxy Trimethyl Ammonium Bromide
D. Calcium Tetra Ammonium Borate

2 The CTAB method is primarily used to isolate genomic DNA from which type of source?

Isolation of Plant genomic DNA using CTAB method Easy
A. Animal blood cells
B. Viral particles
C. Plant tissues
D. Bacterial plasmids

3 What is the chemical nature of CTAB?

Isolation of Plant genomic DNA using CTAB method Easy
A. An anionic detergent
B. A non-ionic detergent
C. A neutral salt
D. A cationic detergent

4 Why is CTAB particularly useful for plant DNA isolation?

Isolation of Plant genomic DNA using CTAB method Easy
A. It removes polysaccharides efficiently
B. It amplifies the DNA
C. It labels the DNA fluorescently
D. It sequences the DNA

5 Which step is usually performed first to release DNA from plant cells?

Isolation of Plant genomic DNA using CTAB method Easy
A. Centrifugation
B. Grinding tissue in liquid nitrogen
C. Adding ethanol
D. Adding RNase

6 Liquid nitrogen is used in the CTAB protocol mainly to:

Isolation of Plant genomic DNA using CTAB method Easy
A. Digest proteins
B. Precipitate the DNA
C. Neutralize the buffer
D. Freeze and help grind the tissue

7 Which reagent is commonly added to the CTAB buffer to prevent DNA degradation by chelating divalent cations?

Isolation of Plant genomic DNA using CTAB method Easy
A. Chloroform
B. Glucose
C. EDTA
D. Ethanol

8 What is the role of -mercaptoethanol in the CTAB extraction buffer?

Isolation of Plant genomic DNA using CTAB method Easy
A. It precipitates DNA
B. It removes polyphenols and prevents oxidation
C. It stains the DNA
D. It digests RNA

9 Which organic solvent mixture is commonly used to remove proteins during CTAB DNA isolation?

Isolation of Plant genomic DNA using CTAB method Easy
A. Water : ethanol
B. Acetone : methanol
C. Chloroform : isoamyl alcohol
D. Hexane : benzene

10 In the chloroform:isoamyl alcohol mixture, what is the purpose of isoamyl alcohol?

Isolation of Plant genomic DNA using CTAB method Easy
A. Digests proteins enzymatically
B. Adds color to the sample
C. Reduces foaming and stabilizes the interface
D. Precipitates the DNA

11 After centrifugation with chloroform, where is the DNA found?

Isolation of Plant genomic DNA using CTAB method Easy
A. Interphase pellet
B. Floating on top
C. Upper aqueous phase
D. Lower organic phase

12 Which reagent is typically used to precipitate DNA after extraction?

Isolation of Plant genomic DNA using CTAB method Easy
A. Chilled isopropanol
B. Chloroform
C. -mercaptoethanol
D. CTAB buffer

13 Cold ethanol used in DNA precipitation is usually of what concentration?

Isolation of Plant genomic DNA using CTAB method Easy
A. 25% for staining
B. 5% for dilution
C. 70% for washing the pellet
D. 10% for lysis

14 Which enzyme is added to remove contaminating RNA from the DNA sample?

Isolation of Plant genomic DNA using CTAB method Easy
A. RNase
B. Lysozyme
C. Proteinase K
D. DNase

15 What is the main function of the CTAB detergent during cell lysis?

Isolation of Plant genomic DNA using CTAB method Easy
A. Cuts DNA at specific sites
B. Adds fluorescent tags to DNA
C. Amplifies DNA fragments
D. Breaks membranes and forms complexes with polysaccharides

16 At what temperature is the plant tissue commonly incubated with CTAB buffer?

Isolation of Plant genomic DNA using CTAB method Easy
A.
B.
C.
D.

17 The final DNA pellet is usually dissolved in which buffer for storage?

Isolation of Plant genomic DNA using CTAB method Easy
A. CTAB buffer
B. TE buffer
C. Chloroform
D. Phosphate saline

18 Which component in plants makes DNA isolation difficult and is specifically targeted by CTAB?

Isolation of Plant genomic DNA using CTAB method Easy
A. Chlorophyll pigments only
B. Nuclear membranes
C. Polysaccharides
D. Ribosomes

19 Which technique is commonly used to check the quality of isolated genomic DNA?

Isolation of Plant genomic DNA using CTAB method Easy
A. Mass spectrometry
B. X-ray crystallography
C. Agarose gel electrophoresis
D. Flow cytometry

20 A pure DNA sample typically shows an ratio of approximately:

Isolation of Plant genomic DNA using CTAB method Easy
A. 1.0
B. 3.0
C. 0.5
D. 1.8

21 In the CTAB method, the primary role of the cationic detergent CTAB (cetyltrimethylammonium bromide) is to:

Isolation of Plant genomic DNA using CTAB method Medium
A. Form complexes with polysaccharides and cell debris that can be separated from DNA under high salt conditions
B. Precipitate DNA directly out of the aqueous solution as an insoluble salt
C. Digest cell wall polysaccharides through enzymatic cleavage
D. Neutralize the negative charge on RNA molecules only

22 Why is a high salt concentration (typically M NaCl) maintained in the CTAB extraction buffer?

Isolation of Plant genomic DNA using CTAB method Medium
A. To keep DNA soluble while allowing CTAB-polysaccharide complexes to be removed
B. To precipitate proteins directly onto the tube wall
C. To completely inhibit the activity of all cellular enzymes instantly
D. To increase the pH of the buffer above 10 for lysis

23 During CTAB DNA extraction, why is the plant tissue typically ground in liquid nitrogen before adding extraction buffer?

Isolation of Plant genomic DNA using CTAB method Medium
A. To dissolve the polysaccharides completely before lysis
B. To precipitate the genomic DNA within the intact cell
C. To oxidize phenolic compounds and remove them
D. To rupture cell walls and inactivate nucleases by keeping the tissue frozen

24 A student adds -mercaptoethanol (or PVP) to the CTAB buffer. What problem is this addressing?

Isolation of Plant genomic DNA using CTAB method Medium
A. Insufficient lysis of the plasma membrane
B. Oxidation of polyphenols that can bind and damage DNA
C. Precipitation of DNA at low temperature
D. Excess RNA contamination in the sample

25 The chloroform:isoamyl alcohol (24:1) step in the CTAB protocol primarily serves to:

Isolation of Plant genomic DNA using CTAB method Medium
A. Dissolve the CTAB detergent completely from the sample
B. Precipitate the DNA into the organic layer for collection
C. Digest residual RNA present in the extract
D. Denature and separate proteins from the aqueous DNA phase while isoamyl alcohol reduces foaming

26 After the chloroform extraction, in which phase is the genomic DNA located, and why?

Isolation of Plant genomic DNA using CTAB method Medium
A. The interphase, because DNA sticks to denatured protein
B. Distributed equally in both phases
C. Upper aqueous phase, because DNA is hydrophilic and negatively charged
D. Lower organic phase, because DNA binds chloroform

27 Isopropanol (or chilled ethanol) is added to the recovered aqueous phase to precipitate DNA. What is the principle behind this?

Isolation of Plant genomic DNA using CTAB method Medium
A. Alcohol raises the temperature, denaturing the DNA
B. Alcohol chemically bonds to DNA bases making it insoluble
C. Alcohol dissolves the CTAB, releasing free DNA
D. Alcohol reduces DNA solubility, allowing salt to neutralize phosphates and DNA to aggregate

28 Why is chilled isopropanol/ethanol preferred over room-temperature alcohol for DNA precipitation?

Isolation of Plant genomic DNA using CTAB method Medium
A. Low temperature increases the DNA solubility in alcohol
B. Cold alcohol degrades contaminating RNA faster
C. Cold alcohol raises the pH of the solution
D. Low temperature improves precipitation efficiency and DNA recovery

29 The DNA pellet is washed with 70% ethanol rather than absolute (100%) ethanol. The main reason is:

Isolation of Plant genomic DNA using CTAB method Medium
A. 70% ethanol digests the remaining proteins
B. 100% ethanol cannot precipitate any nucleic acid
C. 70% ethanol removes residual salts while keeping DNA precipitated
D. 70% ethanol fully dissolves the DNA for purification

30 RNase A is often added during or after the CTAB extraction. Its purpose is to:

Isolation of Plant genomic DNA using CTAB method Medium
A. Precipitate proteins from the aqueous phase
B. Degrade contaminating RNA to yield purer genomic DNA
C. Break down the plant cell wall polysaccharides
D. Remove residual CTAB detergent from the sample

31 A DNA sample isolated by CTAB shows an ratio of 1.6. This most likely indicates:

Isolation of Plant genomic DNA using CTAB method Medium
A. Protein or phenol contamination in the sample
B. Pure, high-quality double-stranded DNA
C. Complete absence of any nucleic acid
D. Excess RNA contamination only

32 Why is the CTAB method generally preferred over standard SDS-based lysis for many plant tissues?

Isolation of Plant genomic DNA using CTAB method Medium
A. CTAB effectively removes polysaccharides and polyphenols abundant in plant cells
B. CTAB works only in the absence of any salt
C. CTAB digests the plant cell wall enzymatically
D. CTAB avoids the need for any organic solvent extraction

33 The CTAB extraction buffer is usually incubated at – for about 30–60 minutes. This incubation primarily:

Isolation of Plant genomic DNA using CTAB method Medium
A. Activates nucleases to fragment the DNA uniformly
B. Precipitates polysaccharides out of solution immediately
C. Enhances cell lysis and CTAB activity while keeping DNA stable
D. Denatures the genomic DNA into single strands permanently

34 EDTA is included in the CTAB extraction buffer mainly to:

Isolation of Plant genomic DNA using CTAB method Medium
A. Chelate divalent cations, thereby inhibiting -dependent nucleases
B. Lyse the plant cell wall directly
C. Precipitate DNA at the end of extraction
D. Provide the high salt needed to solubilize DNA

35 Tris-HCl in the CTAB buffer (usually pH 8.0) functions to:

Isolation of Plant genomic DNA using CTAB method Medium
A. Serve as the reducing agent against polyphenols
B. Provide the divalent cations needed for lysis
C. Directly precipitate the DNA during lysis
D. Maintain a stable pH that keeps DNA soluble and nucleases suppressed

36 If a researcher observes a brown, viscous DNA pellet after CTAB extraction, the most probable cause is:

Isolation of Plant genomic DNA using CTAB method Medium
A. Excess pure genomic DNA in the sample
B. Presence of too much RNase in the buffer
C. Co-precipitation of oxidized polyphenols and polysaccharides
D. Complete degradation of the DNA by nucleases

37 During DNA precipitation, lowering the salt concentration below ~0.5 M in the presence of CTAB causes:

Isolation of Plant genomic DNA using CTAB method Medium
A. CTAB to form insoluble complexes with the DNA, aiding precipitation
B. Proteins to renature and bind the DNA
C. RNA to selectively precipitate while DNA stays in solution
D. DNA to fully dissolve and be lost in solution

38 To estimate DNA concentration, a purified CTAB sample gives an of (double-stranded DNA, 1 cm path). Using the convention that corresponds to , the concentration is:

Isolation of Plant genomic DNA using CTAB method Medium
A.
B.
C.
D.

39 The recovered DNA pellet is finally dissolved in TE buffer rather than in distilled water because TE buffer:

Isolation of Plant genomic DNA using CTAB method Medium
A. Removes any remaining CTAB completely
B. Precipitates residual proteins from the DNA
C. Fragments the DNA to a uniform size
D. Buffers the pH and its EDTA inhibits nucleases for long-term storage

40 During centrifugation after chloroform extraction, why must the aqueous phase be pipetted carefully without disturbing the interphase?

Isolation of Plant genomic DNA using CTAB method Medium
A. The interphase contains denatured proteins and debris that would contaminate the DNA
B. The interphase contains the isopropanol needed later
C. The interphase holds the purest DNA fraction
D. The interphase is where RNase accumulates

41 During CTAB extraction of a leaf sample rich in polysaccharides, the aqueous phase remains highly viscous and DNA fails to spool cleanly at the precipitation step. Which modification is the most rational corrective action?

Isolation of Plant genomic DNA using CTAB method Hard
A. Replace isopropanol with ethanol to selectively precipitate only nucleic acids
B. Increase the NaCl concentration in the extraction buffer to around M to keep polysaccharides soluble in the aqueous phase
C. Lower the extraction temperature from C to C to reduce nuclease activity
D. Add more -mercaptoethanol to oxidize the contaminating polysaccharides

42 CTAB forms an insoluble complex with nucleic acids specifically when the ionic strength of the solution falls below a threshold. In the standard protocol, at which stage is this low-salt CTAB–DNA precipitation deliberately exploited?

Isolation of Plant genomic DNA using CTAB method Hard
A. When the sample is diluted or salt is lowered, causing CTAB–nucleic acid complexes to precipitate away from soluble contaminants
B. During the final ethanol wash of the DNA pellet
C. During the initial C incubation with high-salt CTAB buffer
D. During the chloroform:isoamyl alcohol emulsification step

43 A student measures and for CTAB-extracted DNA. What does this profile most strongly indicate?

Isolation of Plant genomic DNA using CTAB method Hard
A. Protein contamination (low ) plus carbohydrate/CTAB or phenolic contamination (very low )
B. Highly pure DNA with no contaminants present
C. Degraded DNA fragments only, with no chemical contaminants
D. Pure RNA contamination raising both ratios above normal

44 Why is -mercaptoethanol (or DTT) added to the CTAB extraction buffer just before use rather than stored premixed?

Isolation of Plant genomic DNA using CTAB method Hard
A. It binds DNA irreversibly if incubated too long in the buffer
B. It raises the pH of the buffer above during storage
C. It precipitates CTAB if left in solution for extended periods
D. It is a volatile reducing agent that oxidizes and loses its ability to break disulfide bonds and neutralize phenolic oxidation over time

45 Extraction of DNA from a plant species with very high polyphenol content yields brown, oxidized DNA that resists enzymatic digestion. Beyond -mercaptoethanol, which additive is most appropriate to bind polyphenols?

Isolation of Plant genomic DNA using CTAB method Hard
A. Ethylenediaminetetraacetic acid (EDTA)
B. Polyvinylpyrrolidone (PVP)
C. Sodium dodecyl sulfate (SDS)
D. Sodium acetate

46 What is the primary role of EDTA in the CTAB extraction buffer during plant genomic DNA isolation?

Isolation of Plant genomic DNA using CTAB method Hard
A. Chelating divalent cations such as to inhibit -dependent DNase activity
B. Denaturing proteins by disrupting their hydrophobic cores
C. Solubilizing polysaccharides in the aqueous phase
D. Precipitating DNA by neutralizing its negative charge

47 In the chloroform:isoamyl alcohol () step, what is the specific function of the isoamyl alcohol component?

Isolation of Plant genomic DNA using CTAB method Hard
A. It dissolves polysaccharides into the organic phase
B. It reduces foaming and stabilizes the interface between aqueous and organic phases for cleaner separation
C. It precipitates DNA at the phase boundary
D. It denatures proteins more effectively than chloroform alone

48 A protocol calls for precipitating DNA with – volumes of isopropanol rather than – volumes of ethanol. What is the main advantage of isopropanol here?

Isolation of Plant genomic DNA using CTAB method Hard
A. It removes residual proteins better than ethanol
B. It denatures nucleases during precipitation
C. It selectively precipitates RNA over DNA
D. It precipitates DNA efficiently at lower volumes, reducing tube volume while precipitating fewer salts and small polysaccharides

49 Why is the DNA pellet washed with ethanol rather than absolute () ethanol at the final wash step?

Isolation of Plant genomic DNA using CTAB method Hard
A. ethanol removes residual salts and CTAB while keeping DNA precipitated, since DNA would dissolve in more aqueous solutions and salts stay trapped in absolute ethanol
B. ethanol chemically inactivates any remaining DNase enzymes
C. ethanol precipitates the DNA more tightly than absolute ethanol
D. ethanol dissolves the DNA completely and is therefore avoided

50 The CTAB extraction buffer is typically buffered with Tris-HCl at pH . Why is a slightly alkaline pH preferred over acidic conditions?

Isolation of Plant genomic DNA using CTAB method Hard
A. Alkaline pH keeps DNA stable and deprotonated while favoring DNA partition into the aqueous phase during organic extraction
B. Alkaline pH is required to activate proteinase enzymes in the buffer
C. Acidic pH would precipitate CTAB out of solution immediately
D. Acidic pH would raise the melting temperature of DNA excessively

51 Genomic DNA on an agarose gel shows a smear extending far below the high-molecular-weight band expected. During which step is mechanical shearing most likely introduced?

Isolation of Plant genomic DNA using CTAB method Hard
A. The ethanol wash
B. The addition of RNase A after resuspension
C. The C incubation with CTAB buffer
D. Vigorous vortexing or aggressive pipetting of the DNA-containing aqueous phase

52 RNase A treatment is often performed after resuspending the CTAB-isolated DNA rather than being added to the initial extraction buffer. What is the primary reason?

Isolation of Plant genomic DNA using CTAB method Hard
A. RNase A is destroyed by the C extraction temperature
B. RNase A is most active and the DNA is cleaner in the low-viscosity resuspension buffer, and adding it late avoids inhibition by CTAB and cellular debris
C. RNase A precipitates in the presence of high salt buffers
D. RNase A would digest genomic DNA if added at the start

53 A researcher scales the CTAB protocol from mg to g of leaf tissue but keeps buffer volume constant. The yield per gram drops and the lysate is extremely viscous. What is the best explanation?

Isolation of Plant genomic DNA using CTAB method Hard
A. Insufficient buffer volume gives an inadequate CTAB-to-tissue ratio, causing incomplete lysis and inefficient contaminant separation
B. The excess tissue lowers the salt concentration enough to precipitate DNA prematurely
C. Larger tissue mass shifts DNA into the organic phase
D. Too much tissue automatically activates endogenous nucleases

54 Why is fresh or flash-frozen tissue ground in liquid nitrogen preferred over thawed tissue for CTAB DNA extraction?

Isolation of Plant genomic DNA using CTAB method Hard
A. Frozen grinding increases the salt concentration inside the buffer
B. Liquid nitrogen chemically crosslinks proteins to aid their removal
C. Thawed tissue increases the ratio artificially
D. Freezing and grinding disrupt cell walls while keeping tissue frozen inactivates nucleases, preserving high-molecular-weight DNA

55 Given for a diluted DNA sample (dsDNA factor per unit, cm path), what is the concentration of the original undiluted stock?

Isolation of Plant genomic DNA using CTAB method Hard
A.
B.
C.
D.

56 The extraction step is carried out at –C. Which combination of purposes does this incubation temperature serve?

Isolation of Plant genomic DNA using CTAB method Hard
A. It activates RNase already present in the extraction buffer
B. It melts genomic DNA into single strands to aid purification
C. It enhances CTAB detergent action and membrane disruption while helping denature proteins and reducing DNase activity
D. It evaporates chloroform from the aqueous phase before extraction

57 If DNA co-precipitates with polysaccharides, an effective rescue is to redissolve the pellet in high-salt TE, then reprecipitate. What is the mechanistic basis for this cleanup?

Isolation of Plant genomic DNA using CTAB method Hard
A. High salt converts polysaccharides into a form that binds the tube wall
B. High salt keeps polysaccharide–CTAB complexes soluble so a second precipitation recovers DNA while leaving carbohydrates behind
C. High salt lowers the density of DNA so it floats away from polysaccharides
D. High salt chemically degrades the polysaccharides into monosaccharides

58 Why is the concentration of CTAB in the extraction buffer typically kept around (w/v) rather than much higher?

Isolation of Plant genomic DNA using CTAB method Hard
A. is sufficient for effective lysis and complex formation; excess CTAB increases carryover contamination and can inhibit downstream reactions
B. Higher CTAB would chelate the needed for lysis
C. is the maximum solubility of CTAB in aqueous buffer
D. Higher CTAB would raise the buffer pH into the DNA-denaturing range

59 A CTAB-extracted DNA sample fails to amplify in PCR despite good readings. Diluting the template restores amplification. What is the most likely cause?

Isolation of Plant genomic DNA using CTAB method Hard
A. The DNA was too degraded and dilution repaired the fragments
B. The primers were too concentrated in the undiluted reaction
C. Carryover inhibitors such as residual CTAB, polyphenols, or polysaccharides that block polymerase, diluted below their inhibitory threshold
D. The DNA concentration was too low to be detected before dilution

60 Which statement best explains why CTAB (a cationic detergent) is preferred over SDS (an anionic detergent) for many polysaccharide-rich plant tissues?

Isolation of Plant genomic DNA using CTAB method Hard
A. SDS cannot lyse plant cell membranes at all
B. CTAB directly digests polysaccharides into soluble sugars
C. CTAB selectively complexes and separates polysaccharides and nucleic acids by ionic-strength manipulation, whereas SDS does not offer this differential precipitation
D. SDS binds DNA irreversibly and prevents its recovery
Previous MCQ
Unit 8
Next MCQ
Unit 10